Lithium metal fluorophosphate and preparation thereof

ABSTRACT

The invention provides new and novel lithium-metal-fluorophosphates which, upon electrochemical interaction, release lithium ions, and are capable of reversibly cycling lithium ions. The invention provides a rechargeable lithium battery which comprises an electrode formed from the novel lithium-metal-fluorophosphates. The lithium-metal-fluorophosphates comprise lithium and at least one other metal besides lithium.

DESCRIPTION

This application is a continuation of application Ser. No. 10/045,685filed on Nov. 7, 2001, allowed, which is a continuation of applicationSer. No. 09/559,861 filed on Apr. 27, 2000, which issued on May 14, 2002as U.S. Pat. No. 6,387,568.

FIELD OF THE INVENTION

This invention relates to improved materials usable as electrode activematerials, and electrodes formed from it for electrochemical cells inbatteries.

BACKGROUND OF THE INVENTION

Lithium batteries are prepared from one or more lithium electrochemicalcells containing electrochemically active (electroactive) materials.Such cells typically include an anode (negative electrode), a cathode(positive electrode), and an electrolyte interposed between spaced apartpositive and negative electrodes. Batteries with anodes of metalliclithium and containing metal chalcogenide cathode active material areknown. The electrolyte typically comprises a salt of lithium dissolvedin one or more solvents, typically nonaqueous (aprotic) organicsolvents. Other electrolytes are solid electrolytes typically calledpolymeric matrixes that contain an ionic conductive medium, typically ametallic powder or salt, in combination with a polymer that itself maybe ionically conductive which is electrically insulating. By convention,during discharge of the cell, the negative electrode of the cell isdefined as the anode. Cells having a metallic lithium anode and metalchalcogenide cathode are charged in an initial condition. Duringdischarge, lithium ions from the metallic anode pass through the liquidelectrolyte to the electrochemically active (electroactive) material ofthe cathode whereupon they release electrical energy to an externalcircuit.

It has recently been suggested to replace the lithium metal anode withan insertion anode, such as a lithium metal chalcogenide or lithiummetal oxide. Carbon anodes, such as coke and graphite, are alsoinsertion materials. Such negative electrodes are used withlithium-containing insertion cathodes, in order to form an electroactivecouple in a cell. Such cells, in an initial condition, are not charged.In order to be used to deliver electrochemical energy, such cells mustbe charged in order to transfer lithium to the anode from thelithium-containing cathode. During discharge the lithium is transferredfrom the anode back to the cathode. During a subsequent recharge, thelithium is transferred back to the anode where it reinserts. Uponsubsequent charge and discharge, the lithium ions (Li⁺) are transportedbetween the electrodes. Such rechargeable batteries, having no freemetallic species are called rechargeable ion batteries or rocking chairbatteries. See U.S. Pat. Nos. 5,418,090; 4,464,447; 4,194,062; and5,130,211.

Preferred positive electrode active materials include LiCoO₂, LiMn₂O₄,and LiNiO₂. The cobalt compounds are relatively expensive and the nickelcompounds are difficult to synthesize. A relatively economical positiveelectrode is LiMn₂O₄, for which methods of synthesis are known. Thelithium cobalt oxide (LiCoO₂), the lithium manganese oxide (LiMn₂O₄),and the lithium nickel oxide (LiNiO₂) all have a common disadvantage inthat the charge capacity of a cell comprising such cathodes suffers asignificant loss in capacity. That is, the initial capacity available(amp hours/gram) from LiMn₂O₄, LiNiO₂, and LiCoO₂ is less than thetheoretical capacity because significantly less than 1 atomic unit oflithium engages in the electrochemical reaction. Such an initialcapacity value is significantly diminished during the first cycleoperation and such capacity further diminishes on every successive cycleof operation. For LiNiO₂ and LiCoO₂ only about 0.5 atomic units oflithium is reversibly cycled during cell operation. Many attempts havebeen made to reduce capacity fading, for example, as described in U.S.Pat. No. 4,828,834 by Nagaura et al. However, the presently known andcommonly used, alkali transition metal oxide compounds suffer fromrelatively low capacity. Therefore, there remains the difficulty ofobtaining a lithium-containing electrode material having acceptablecapacity without disadvantage of significant capacity loss when used ina cell.

SUMMARY OF THE INVENTION

The invention provides novel lithium-metal-fluorophosphate materialswhich, upon electrochemical interaction, release lithium ions, and arecapable of reversibly cycling lithium ions. The invention provides arechargeable lithium battery which comprises an electrode formed fromthe novel lithium-metal-fluorophosphates. Methods for making the novellithium-metal-fluorophosphates and methods for using suchlithium-metal-fluorophosphates in electrochemical cells are alsoprovided. Accordingly, the invention provides a rechargeable lithiumbattery which comprises an electrolyte; a first electrode having acompatible active material; and a second electrode comprising the novellithium-metal-fluorophosphate materials. The novel materials, preferablyused as a positive electrode active material, reversibly cycle lithiumions with the compatible negative electrode active material. Desirably,the lithium-metal-fluorophosphate is represented by the nominal generalformula LiM_(1-y)Ml_(y)PO₄F where 0≦y≦1. Such compounds include LiMPO₄Ffor y=0. Such compounds are also represented by Li_(1-x)MPO₄F andLi_(1-x)M_(1-y)Ml_(y)PO₄F, where in an initial condition, “x” isessentially zero; and during cycling a quantity of “x” lithium isreleased where 0≦x≦1. Correspondingly, M has more than one oxidationstate in the lithium-metal-fluorophosphate compound, and more than oneoxidation state above the ground state M⁰. The term oxidation state andvalence state are used in the art interchangeably. Also, Ml may havemore than one oxidation state, and more than one oxidation state abovethe ground state Ml^(o).

Desirably, M is selected from V (vanadium), Cr (chromium), Fe (iron), Ti(titanium), Mn (manganese), Co (cobalt), Ni (nickel), Nb (niobium), Mo(molybdenum), Ru (ruthenium), Rh (rhodium) and mixtures thereof.Preferably, M is selected from the group V, Cr, Fe, Ti, Mn, Co, and Ni.As can be seen, M is preferably selected from the first row oftransition metals, and M preferably initially has a +3 oxidation state.In another preferred aspect, M is a metal having a +3 oxidation stateand having more than one oxidation state, and is oxidizable from itsoxidation state in lithium-metal-fluorophosphate compound. In anotheraspect, Ml is a metal having a +3 oxidation state, and desirably Ml isan element selected from the group V, Cr, Fe, Ti, Mn, Co, Ni, Nb, Mo,Ru, Rh, B (boron) and Al (aluminum).

In a preferred aspect, the product LiM_(1-y)Ml_(y)PO₄F is a triclinicstructure. In another aspect, the “nominal general formula” refers tothe fact that the relative proportions of the atomic species may varyslightly on the order of up to 5 percent, or more typically, 1 percentto 3 percent. In another aspect the term “general” refers to the familyof compounds with M, Ml, and y representing variations therein. Theexpressions y and 1-y signify that the relative amount of M and Ml mayvary and that 0≦y≦1. In addition, M may be a mixture of metals meetingthe earlier stated criteria for M. In addition, Ml may be a mixture ofelements meeting the earlier stated criteria for Ml.

The active material of the counter electrode is any material compatiblewith the lithium-metal-fluorophosphate of the invention. Where thelithium-metal-fluorophosphate is used as a positive electrode activematerial, metallic lithium may be used as the negative electrode activematerial where lithium is removed and added to the metallic negativeelectrode during use of the cell. The negative electrode is desirably anonmetallic insertion compound. Desirably, the negative electrodecomprises an active material from the group consisting of metal oxide,particularly transition metal oxide, metal chalcogenide, carbon,graphite, and mixtures thereof. It is preferred that the anode activematerial comprises a carbonaceous material such as graphite. Thelithium-metal-fluorophosphate of the invention may also be used as anegative electrode material.

The starting (precursor) materials include a lithium containingcompound, and a metal phosphate compound. Preferably, the lithiumcontaining compound is in particle form, and an example is lithium salt.A particular example of a lithium salt is lithium fluoride (LiF).Preferably, the metal phosphate compound is in particle form, andexamples include metal phosphate salt, such as FePO₄ and CrPO₄. Thelithium compound and the metal phosphate compound are mixed in aproportion which provides the stated general formula.

In one aspect, the starting materials are intimately mixed and thenreacted together where the reaction is initiated by heat. The mixedpowders are pressed into a pellet. The pellet is then heated to anelevated temperature. This reaction can be run under an air atmosphere,or can be run under a non-oxidizing atmosphere. The precursors arecommercially available, and include, for example, a lithium fluoridesalt, and metal phosphate, such as CrPO₄, FePO₄, or MnPO₄.

In another aspect, the metal phosphate salt used as a precursor for thelithium metal phosphate reaction can be formed either by a carbothermalreaction, or by a hydrogen reduction reaction. Preferably, thephosphate-containing anion compound is in particle form, and examplesinclude metal phosphate salt, diammonium hydrogen phosphate (DAHP), andammonium dihydrogen phosphate (ADHP). The metal compound for making theprecursor are typically metal oxides. In the carbothermal reaction, thestarting materials are mixed together with carbon, which is included inan amount sufficient to reduce the metal oxide to metal phosphate. Thestarting materials for the formation of the metal phosphates aregenerally crystals, granules, and powders and are generally referred toas being in particle form. Although many types of phosphate salts areknown, it is preferred to use diammonium hydrogen phosphate (DAHP), orammonium dihydrogen phosphate (ADHP). Both DAHP and ADHP meet thepreferred criteria that the starting materials decompose to liberate thephosphate anion which may then react with the metal oxide compound.Exemplary metal compounds are Fe₂O₃, Fe₃O₄, V₂O₅, VO₂, MnO₂, Mn₂O₃,TiO₂, Ti₂O₃, Cr₂O₃, CoO, Ni₃(PO₄)₂, Nb₂O₅, Mo₂O₃, V₂O₃, FeO, CO₃O₄,CrO₃, Nb₂O₃, MoO₃. The starting materials are available from a number ofsources. For example, the metal oxides, such as vanadium pentoxide oriron oxide, are available from suppliers including Kerr McGee, JohnsonMatthey, or Alpha Products of Davers, Mass.

Objects, features, and advantages of the invention include anelectrochemical cell or battery based on lithium-metal-fluorophosphates.Another object is to provide a cathode active material which combinesthe advantages of good discharge capacity and capacity retention. It isalso an object of the present invention to provide positive electrodeswhich can be manufactured economically. Another object is to provide acathode active material which can be rapidly and cheaply produced andlends itself to commercial scale production for preparation of largequantities.

These and other objects, features, and advantages will become apparentfrom the following description of the preferred embodiments, claims, andaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the results of an x-ray diffraction analysis, of LiVPO₄Fprepared as above, using CuKα radiation, λ=1.5404 Å. Bars refer tosimulated pattern from refined cell parameters SG=P−1 (triclinic) (1).The values are a=5.1738 Å (0.002), b=5.3096 Å (0.002), c=7.2503 Å(0.001); the angle α=72.4794 (0.06), β=107.7677 (0.04), γ=81.3757(0.04), cell volume=174.35 Å³. The crystal system is triclinic.

FIG. 2 is a voltage/capacity plot of LiVPO₄F containing cathode cycledwith a lithium metal anode in a range of 3.0 to 4.4 volts. The cathodecontained 29.4 mg of LiVPO₄F active material prepared by the methoddescribed above.

FIG. 3 displays the differential capacity during cell charge anddischarge vs. cell voltage for the electrochemical cell containingLiVPO₄F.

FIG. 4 shows the results of an x-ray diffraction analysis, of LiFePO₄Fprepared as above, using CuKα radiation, λ=1.5404 Å. Bars refer tosimulated pattern from refined cell parameters SG=P−1 (triclinic). Thevalues are a=5.1528 Å (0.002), b=5.3031 Å (0.002), c=7.4966 Å (0.003);the angle α=67.001 (0.02), β=67.164° (0.03), γ=81.512° (0.02), cellvolume=173.79 Å³. The crystal system is triclinic.

FIG. 5 shows the results of an x-ray diffraction analysis, of LiTiPO₄Fprepared as above, using CuKα radiation, λ=1.5404 Å. The x-raydiffraction pattern was triclinic.

FIG. 6 shows the results of an x-ray diffraction analysis, of LiCrPO₄Fprepared as above, using CuKα radiation, λ=1.5404 Å. Bars refer tosimulated pattern from refined cell parameters SG=P−1 (triclinic). Thevalues are a=4.996 Å (0.002), b=5.307 Å (0.002), α=6.923 Å (0.004); theangle α=71.600° (0.06), β=100.71° (0.04), γ=78.546° (0.05), cellvolume=164.54 Å³. The crystal system is triclinic.

FIG. 7 is a diagrammatic representation of a typical laminatedlithium-ion battery cell structure.

FIG. 8 is a diagrammatic representation of a typical multi-cell batterycell structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides lithium-metal-fluorophosphates, which areusable as electrode active materials, for lithium (Li⁺) ion removal andinsertion. Upon extraction of the lithium ions from thelithium-metal-fluorophosphates, significant capacity is achieved. In oneaspect of the invention, electrochemical energy is provided whencombined with a suitable counter electrode by extraction of a quantity xof lithium from lithium-metal-fluorophosphates LiM_(1-y)Ml_(y)PO₄F. Whena quantity of lithium is removed per formula unit of thelithium-metal-fluorophosphate, metal M is oxidized. Accordingly, duringcycling, charge and discharge, the value of x varies as x greater thanor equal to 0 and less than or equal to 1.

In another aspect, the invention provides a lithium ion battery whichcomprises an electrolyte; a negative electrode having an insertionactive material; and a positive electrode comprising alithium-metal-fluorophosphate active material characterized by anability to release lithium ions for insertion into the negativeelectrode active material. The lithium-metal-fluorophosphate isdesirably represented by the aforesaid nominal general formulaLiM_(1-y)Ml_(y)PO₄F. Desirably, the metal M is selected from the group:Ti, V, Cr, Mn, Fe, Co, Ni, Nb, Mo, and mixtures thereof. Preferably themetal M is selected from the group: Ti, V, Cr, Mn, Fe, Co, Ni, andmixtures thereof. Although the metals M and Ml may be the same, it ispreferred that M and Ml be different, and desirably Ml is an elementselected from the group: Ti, V, Cr, Mn, Fe, Co, Ni, Nb, Mo, Al, B, andmixtures thereof.

The present invention provides a new material, a lithium metalfluorophosphate, and demonstrates that with this new materialsignificant capacity as a cathode active material is utilizable andmaintained.

A preferred approach for making the LiM_(1-y)Ml_(y)PO₄F is a two stagedapproach (Example I). The first stage (Reaction 1a) involves thecreation of the metal phosphate precursor, followed by the second stage(Reaction 1b) of reacting the metal phosphate with the commerciallyavailable lithium fluoride to produce the lithium metal fluorophosphate.The basic procedure is described with reference to exemplary startingmaterials, but is not limited thereby. In the first stage, the basicprocess comprises reacting a metal compound, for example vanadiumpentoxide or ferric oxide, with a phosphoric acid derivative, preferablya phosphoric acid ammonium salt, such as ammonium dihydrogen phosphate(ADHP) or diammonium hydrogen phosphate (DAHP). The powders wereintimately mixed and dry ground for about 30 minutes to form ahomogeneous mixture of the starting materials. Then the mixed powderswere pressed into pellets. The reaction was conducted by heating thepellets in an oven at a preferred heating rate to an elevatedtemperature, and held at such elevated temperature for several hours. Apreferred ramp rate of 2° C./minute was used to heat to a preferredtemperature of 300° C. The reaction was carried out under a reducingatmosphere of hydrogen gas. The flow rate will depend on the size of theoven and the quantity needed to maintain the atmosphere. The pelletswere allowed to cool to ambient temperature, then re-ground andrepressed into pellets. The reaction was continued by reheating thepellets in an oven at a preferred heating rate to a second elevatedtemperature, and held at such elevated temperature for several hours tocomplete the reaction. A preferred ramp rate of 2° C./minute was used toheat to a preferred second elevated temperature is 850° C. The reactionwas carried out under a reducing atmosphere of hydrogen gas. The pelletswere then allowed to cool to ambient temperature. A preferred rate ofcooling was about 2° C./minute.

A preferred approach for the second stage (Reaction 1b) for making theLiM_(1-y)Ml_(y)PO₄F is to start with the commercially availableprecursor, lithium fluoride LiF and mix with the metal phosphate MPO₄.The precursors were intimately mixed and dry ground for about 30minutes. The mixture was then pressed into pellets. Reaction wasconducted by heating in an oven at a preferred ramped heating rate to anelevated temperature, and held at such elevated temperature for fifteenminutes to complete formation of the reaction product. A preferred ramprate of 2° C./minute was used to heat to a preferred temperature of 700°C. The entire reaction was conducted under a normal air atmosphere. Acovered nickel crucible to limit oxygen availability was used. In analternative, a covered ceramic crucible can be used. The pellet wasremoved from the oven and allowed to cool to room temperature. Preferredcooling rates are from about 2° C./minute to about 60° C./minute, with amore preferred rate of about 50° C./minute.

In another variation, the precursor metal phosphate was created prior tothe creation of the lithium-metal-fluorophosphate using the carbothermalmethod in a two staged approach (Example 11). The first stage (Reaction2a) involves the creation of the metal phosphate precursor, followed bythe second stage of reacting the metal phosphate with the commerciallyavailable lithium fluoride to produce the lithium metal fluorophosphate.The basic procedure is described with reference to exemplary startingmaterials, but is not limited thereby. In the first stage, the basicprocess comprises reacting a metal compound, for example vanadiumpentoxide or ferric oxide, with a phosphoric acid derivative, preferablya phosphoric acid ammonium salt, such as ammonium dihydrogen phosphate(ADHP) or diammonium hydrogen phosphate (DAHP). The powders wereintimately mixed and dry ground for about 30 minutes to form ahomogeneous mixture of the starting materials. Then the mixed powderswere pressed into pellets. The reaction was conducted by heating thepellets in an oven at a preferred heating rate to an elevatedtemperature, and held at such elevated temperature for several hours. Apreferred ramp rate of 2° C./minute was used to heat to a preferredtemperature of 300° C.

The reaction was carried out under a non-oxidizing atmosphere of argongas. The flow rate will depend on the size of the oven and the quantityneeded to maintain the atmosphere.

The pellets were allowed to cool to ambient temperature, then re-groundand repressed into pellets. The reaction was continued by reheating thepellets in an oven at a preferred heating rate to a second elevatedtemperature, and held at such elevated temperature for several hours tocomplete the reaction. A preferred ramp rate of 2° C./minute was used toheat to a preferred second elevated temperature was 850° C. The reactionwas carried out under a non-oxidizing atmosphere of argon gas. Afterheating for a preferred time of 8 hours, the pellets were allowed tocool to ambient temperature at a preferred rate of 2° C./minute.

A preferred approach for the second stage (Example 11, Reaction 2b) formaking the LiM_(1-y)Ml_(y)PO₄F is to start with the commerciallyavailable precursor, lithium fluoride LiF and mix with the metalphosphate MPO₄. The precursors were intimately mixed and dry ground for30 minutes. The mixture was then pressed into pellets. Reaction wasconducted by heating in an oven at a preferred ramped heating rate to anelevated temperature, and held at such elevated temperature for fifteenminutes to complete formation of the reaction product. A preferred ramprate of 2° C./minute was used to heat to a preferred temperature of 700°C. The entire reaction was conducted under an air atmosphere, but acovered crucible was used to limit oxygen availability. The pellet wasremoved from the oven and allowed to cool to room temperature.

In a variation of the second stage, lithium carbonate and ammoniumfluoride were used in place of lithium fluoride (Example IV). Theprecursors were intimately mixed and dry ground for about 30 minutes.The mixture is then pressed into pellets. Reaction was conducted byheating in an oven at a preferred ramped heating rate (of 2° C./minute)to an elevated temperature, and held at such elevated temperature forabout 15 minutes to complete formation of the reaction product. Apreferred elevated temperature was 700° C. The reaction was conductedunder an air atmosphere in a covered crucible to limit oxygenavailability. The pellet was removed from the oven and allowed to coolto room temperature. Refer to Reaction 4 herein.

A process for making lithium mixed-metal fluorophosphate, such aslithium aluminum vanadium fluorophosphate, the precursors aluminumphosphate and vanadium phosphate were made separately, then mixed withlithium fluoride (Example III, Reaction 3b). The vanadium phosphate wasmade as described in reaction 1(a) or reaction 2(a). The basic procedurefor making aluminum phosphate is described with reference to exemplarystarting materials, but is not limited thereby (Example III, Reaction3a). The aluminum phosphate was made by intimately mixing aluminumhydroxide and ammonium dihydrogen phosphate powders, and dry groundingthem for about 30 minutes. The mixed powders were then pressed intopellets. The reaction was conducted by heating the pellets in an oven ata preferred heating rate to an elevated temperature, and held at thatelevated temperature for several hours. The reaction was carried outunder an air atmosphere. The pellets were allowed to cool to ambienttemperature, and then ground into powder. Exemplary and preferred ramprates, elevated reaction temperatures and reaction times are describedherein. In one aspect, a ramp rate of 2° C./minute was used to heat toan elevated temperature of about 950° C. and allowed to dwell for 8hours. The precursor was then allowed to cool to room temperature. Referto Reaction 3(a) herein.

A preferred approach for making the lithium aluminum transition metalfluorophosphate was to use the aluminum phosphate and the transitionmetal phosphate generated above, and mix them with lithium fluoride(Reaction 3b). The powders were intimately mixed and dry ground forabout 30 minutes. The mixture was then pressed into pellets. Reactionwas conducted by heating in an oven at a preferred ramped heating rateto an elevated temperature, and held at such elevated temperature forabout fifteen minutes to complete the formation of the reaction product.The entire reaction was completed under a normal air atmosphere. Thepellet was removed from the oven and allowed to cool to roomtemperature. Exemplary and preferred reaction conditions are describedherein. In one aspect, a ramp rate of 2° C./minute was used to heat toan elevated temperature of 700° C. and was allowed to dwell for 15minutes. Refer to Reaction 3(b) herein. Recent research has indicatedthat doping of materials with non-transition metals or other elements,such as boron, tends to increase the operating voltage. Substitution ofnon-transition elements such as aluminum for transition metals tends tostabilize the structure of cathode active materials. This aids thestability and cyclability of the materials.

The general aspects of the above synthesis route are applicable to avariety of starting materials. The metal compounds are reduced in thepresence of a reducing agent, such as hydrogen or carbon. The sameconsiderations apply to other metal and phosphate containing startingmaterials. The thermodynamic considerations such as ease of reduction,of the selected starting materials, the reaction kinetics, and themelting point of the salts will cause adjustment in the generalprocedure, such as the amount of reducing agent, the temperature of thereaction, and the dwell time.

Referring back to the discussion of the reactions for generating theprecursor metal-phosphates, Reactions 1(a) and 2(a), the reaction isinitially conducted at a relatively low temperature from 200° C. to 500°C., preferably around 300° C., cooled to ambient temperature, thenconducted at a relatively high temperature from 700° C. to a temperaturebelow the melting point of the metal phosphate, preferably around 850°C. The melting point of the metal phosphates is believed to be in therange of 950° C. to 1050° C. It is preferred to heat the startingmaterials at a ramp rate of a fraction of a degree to 10° C. per minuteand preferably about 2° C. per minute. After reaction, the products arecooled to ambient temperature with a cooling rate similar to the ramprate, and preferably around 2° C./minute.

Referring back to the discussion of the lithium fluoride and metalphosphate reaction (Reactions 1b, 2b, 3b, and 4), the temperature shouldbe run at 400° C. or greater but below the melting point of the metalphosphate, and preferably at about 700° C. It is preferred to heat theprecursors at a ramp rate of a fraction of a degree to 10° C. per minuteand preferably about 2° C. per minute. Once the desired temperature isattained, the reactions are held at the reaction temperature from 10minutes to several hours, and preferably around 15 minutes. The timebeing dependent on the reaction temperature chosen. The heating may beconducted under an air atmosphere, or if desired may be conducted undera non-oxidizing or inert atmosphere. After reaction, the products arecooled from the elevated temperature to ambient (room) temperature (i.e.10° C. to 40° C.). Desirably, the cooling occurs at a rate of about 50°C./minute. Such cooling has been found to be adequate to achieve thedesired structure of the final product. It is also possible to quenchthe products at a cooling rate on the order of about 100° C./minute. Insome instances, such rapid cooling may be preferred.

As an alternative to the two stage process for producing the lithiummetal fluorophosphate, a single stage process is used (Example V,Reaction 5). A mixture was made of a metal compound, for examplevanadium pentoxide, ammonium dihydrogen phosphate, lithium fluoride andcarbon. The mixture was dry ground for about 30 minutes to intimatelymix the powders. The powders were pressed into pellets. The reaction wasconducted by heating the pellets in an oven at a preferred rate to afirst elevated temperature for several hours. A preferred temperature is300° C. The reaction was carried out under a non-oxidizing atmosphere.The flow rate will depend on the size of the oven and the quantityneeded to maintain the temperature. The pellets were allowed to cool,then re-ground and repressed into pellets. The reaction was-continued byreheating the pellets in an oven at a preferred heating rate to a secondelevated temperature, and held at such elevated temperature for severalhours to complete the reaction. A preferred second elevated temperatureis 850° C. The reaction was carried out under a non-oxidizingatmosphere. In one aspect, a ramp rate of 2° C./minute was used to heatto an elevated temperature of about 300° C. and allowed to dwell for 3hours. The precursor material was allowed to cool to room temperature,and subsequently heated to 850° C. along with a dwell time of 8 hours.Refer to Reaction 5 herein.

FIGS. 1 through 6 which will be described more particularly below showthe characterization data and capacity in actual use for the cathodematerials (positive electrodes) of the invention. Some tests wereconducted in a cell comprising a lithium metal counter electrode(negative electrode). All of the cells had an EC/DMC (2:1) 1 molar LiPF₆electrolyte.

Typical cell configurations will now be described with reference toFIGS. 7 and 8; and such battery or cell utilizes the novel activematerial of the invention. Note that the preferred cell arrangementdescribed here is illustrative and the invention is not limited thereby.Experiments are often performed, based on full and half cellarrangements, as per the following description. For test purposes, testcells are often fabricated using lithium metal electrodes. When formingcells for use as batteries, it is preferred to use an insertion positiveelectrode as per the invention and a graphitic carbon negativeelectrode.

A typical laminated battery cell structure 10 is depicted in FIG. 7. Itcomprises a negative electrode side 12, a positive electrode side 14,and an electrolyte/separator 16 there between. Negative electrode side12 includes current collector 18, and positive electrode side 14includes current collector 22. A copper collector foil 18, preferably inthe form of an open mesh grid, upon which is laid a negative electrodemembrane 20 comprising an insertion material such as carbon or graphiteor low-voltage lithium insertion compound, dispersed in a polymericbinder matrix. An electrolyte/separator film 16 membrane is preferably aplasticized copolymer. This electrolyte/separator preferably comprises apolymeric separator and a suitable electrolyte for ion transport. Theelectrolyte/separator is positioned upon the electrode element and iscovered with a positive electrode membrane 24 comprising a compositionof a finely divided lithium insertion compound in a polymeric bindermatrix. An aluminum collector foil or grid 22 completes the assembly.Protective bagging material 40 covers the cell and prevents infiltrationof air and moisture.

In another embodiment, a multi-cell battery configuration as per FIG. 8is prepared with copper current collector 51, negative electrode 53,electrolyte/separator 55, positive electrode 57, and aluminum currentcollector 59. Tabs 52 and 58 of the current collector elements formrespective terminals for the battery structure. As used herein, theterms “cell” and “battery” refer to an individual cell comprisinganode/electrolyte/cathode and also refer to a multi-cell arrangement ina stack.

The relative weight proportions of the components of the positiveelectrode are generally: 50-90% by weight active material; 5-30% carbonblack as the electric conductive diluent; and 3-20% binder chosen tohold all particulate materials in contact with one another withoutdegrading ionic conductivity. Stated ranges are not critical, and theamount of active material in an electrode may range from 25-95 weightpercent. The negative electrode comprises about 50-95% by weight of apreferred graphite, with the balance constituted by the binder. Atypical electrolyte separator film comprises approximately two partspolymer for every one part of a preferred fumed silica. The conductivesolvent comprises any number of suitable solvents and salts. Desirablesolvents and salts are described in U.S. Pat. Nos. 5,643,695 and5,418,091. One example is a mixture of EC:DMC:LiPF₆ in a weight ratio ofabout 60:30:10.

Solvents are selected to be used individually or in mixtures, andinclude dimethyl carbonate (DMC), diethylcarbonate (DEC),dipropylcarbonate (DPC), ethylmethylcarbonate (EMC), ethylene carbonate(EC), propylene carbonate (PC), butylene carbonate, lactones, esters,glymes, sulfoxides, sulfolanes, etc. The preferred solvents are EC/DMC,EC/DEC, EC/DPC and EC/EMC The salt content ranges from 5% to 65% byweight, preferably from 8% to 35% by weight.

Those skilled in the art will understand that any number of methods areused to form films from the casting solution using conventional meterbar or doctor blade apparatus. It is usually sufficient to air-dry thefilms at moderate temperature to yield self-supporting films ofcopolymer composition. Lamination of assembled cell structures isaccomplished by conventional means by pressing between metal plates at atemperature of about 120-160° C. Subsequent to lamination, the batterycell material may be stored either with the retained plasticizer or as adry sheet after extraction of the plasticizer with a selectivelow-boiling point solvent.

The plasticizer extraction solvent is not critical, and methanol orether are often used.

Separator membrane element 16 is generally polymeric and prepared from acomposition comprising a copolymer. A preferred composition is the 75 to92% vinylidene fluoride with 8 to 25% hexafluoropropylene copolymer(available commercially from Atochem North America as Kynar FLEX) and anorganic solvent plasticizer. Such a copolymer composition is alsopreferred for the preparation of the electrode membrane elements, sincesubsequent laminate interface compatibility is ensured. The plasticizingsolvent may be one of the various organic compounds commonly used assolvents for electrolyte salts, e.g., propylene carbonate or ethylenecarbonate, as well as mixtures of these compounds. Higher-boilingplasticizer compounds such as dibutyl phthalate, dimethyl phthalate,diethyl phthalate, and tris butoxyethyl phosphate are particularlysuitable. Inorganic filler adjuncts, such as fumed alumina or silanizedfumed silica, may be used to enhance the physical strength and meltviscosity of a separator membrane and, in some compositions, to increasethe subsequent level of electrolyte solution absorption.

In the construction of a lithium-ion battery, a current collector layerof aluminum foil or grid is overlaid with a positive electrode film, ormembrane, separately prepared as a coated layer of a dispersion ofinsertion electrode composition. This is typically an insertion compoundsuch as LiMn₂O₄ (LMO), LiCoO₂, or LiNiO₂, powder in a copolymer matrixsolution, which is dried to form the positive electrode. Anelectrolyte/separator membrane is formed as a dried coating of acomposition comprising a solution containing VdF:HFP copolymer and aplasticizer solvent is then overlaid on the positive electrode film. Anegative electrode membrane formed as a dried coating of a powderedcarbon or other negative electrode material dispersion in a VdF:HFPcopolymer matrix solution is similarly overlaid on the separatormembrane layer. A copper current collector foil or grid is laid upon thenegative electrode layer to complete the cell assembly. Therefore, theVdF:HFP copolymer composition is used as a binder in all of the majorcell components, positive electrode film, negative electrode film, andelectrolyte/separator membrane. The assembled components are then heatedunder pressure to achieve heat-fusion bonding between the plasticizedcopolymer matrix electrode and electrolyte components, and to thecollector grids, to thereby form an effective laminate of cell elements.This produces an essentially unitary and flexible battery cellstructure.

Examples of forming cells containing metallic lithium anode, insertionelectrodes, solid electrolytes and liquid electrolytes can be found inU.S. Pat. Nos. 4,668,595; 4,830,939; 4,935,317; 4,990,413; 4,792,504;5,037,712; 5,262,253; 5,300,373; 5,435,054; 5,463,179; 5,399,447;5,482,795 and 5,411,820; each of which is incorporated herein byreference in its entirety. Note that the older generation of cellscontained organic polymeric and inorganic electrolyte matrix materials,with the polymeric being most preferred. The polyethylene oxide of U.S.Pat. No. 5,411,820 is an example. More modern examples are the VdF:HFPpolymeric matrix. Examples of casting, lamination and formation of cellsusing VdF:HFP are as described in U.S. Pat. Nos. 5,418,091; 5,460,904;5,456,000; and 5,540,741; assigned to Bell Communications Research, eachof which is incorporated herein by reference in its entirety.

As described earlier, the electrochemical cell operated as per theinvention, may be prepared in a variety of ways. In one embodiment, thenegative electrode may be metallic lithium. In more desirableembodiments, the negative electrode is an insertion active material,such as, metal oxides and graphite. When a metal oxide active materialis used, the components of the electrode are the metal oxide,electrically conductive carbon, and binder, in proportions similar tothat described above for the positive electrode. In a preferredembodiment, the negative electrode active material is graphiteparticles. For test purposes, test cells are often fabricated usinglithium metal electrodes. When forming cells for use as batteries, it ispreferred to use an insertion metal oxide positive electrode and agraphitic carbon negative electrode. Various methods for fabricatingelectrochemical cells and batteries and for forming electrode componentsare described herein. The invention is not, however, limited by anyparticular fabrication method.

Formation of Active Materials.

EXAMPLE I

Reaction 1(a)—Using Hydrogen to Form Precursors0.5V₂O₅+NH₄H₂PO₄+H₂→VPO₄+NH₃+2.5H₂O

-   (1) Pre-mix reactants in following proportions using ball mill.    Thus, 0.5 mol V₂O₅=90.94 g and 1.0 mol NH₄H₂PO₄=115.03 g.-   (2) Pelletize the power mixture.-   (3) Heat to 300° C. at a rate of 2° C./minute in a flowing H2    atmosphere. Dwell for 8 hours at 300° C.-   (4) Cool at 2° C./minute to room temperature.-   (5) Powderize and re-pelletize.-   (6) Heat to 850° C. in a flowing H2 atmosphere at a rate of 2°    C./minute. Dwell for 8 hours at 850° C.-   (7) Cool at 2° C./minute to room temperature.

Reaction 1(b)-Formation of Lithium Vanadium FluorophosphateLiF+VPO₄→LiVPO₄F

-   (1) Pre-mix reactants in equi-molar portions using a ball mill.    Thus, 1 mol LiF=25.94 g and 1 mol VPO₄=145.91 g.-   (2) Pelletize powder mixture.-   (3) Heat to 700° C. at a rate of 2° C./minute in an air atmosphere    in a covered nickel crucible. Dwell for 15 minutes at 700° C.-   (4) Cool to room temperature at about 50° C./minute.-   (5) Powderize pellet.

EXAMPLE II

Reaction 2(a)—Using a Carbothermal Method to Form Precursors0.5V₂O₅+NH₄H₂PO₄+C→VPO₄+NH₃+1.5H₂O+CO

-   (1) Pre-mix reactants in the following proportions using ball mill.    Thus, 0.5 mol V₂O₅=90.94 and 1.0 mol NH₄H₂PO₄=115.03 g.-   (2) 1.0 mol carbon=12.0 g (Use 10% excess carbon→13.2 g)-   (3) Pelletize powder mixture-   (4) Heat pellet to 300° C. at a rate of 2° C./minute in an inert    atmosphere (e.g., argon). Dwell for 3 hours at 300° C.-   (5) Cool to room temperature at 2° C./minute.-   (6) Powderize and re-pelletize.-   (7) Heat pellet to 850° C. at a rate of 2° C./minute in an inert    atmosphere (e.g. argon). Dwell for 8 hours at 850° C. under an argon    atmosphere.-   (8) Cool to room temperature at 2° C./minute.-   (9) Powderize pellet.

Reaction 2(b)—Formation of Lithium Vanadium FluorophosphateLiF+VPO₄→LiVPO₄F

-   (1) Pre-mix reactants in equi-molar portions using a ball mill.    Thus, 1 mol LiF=25.94 g and 1 mol VPO₄=145.91 g.-   (2) Pelletize powder mixture.-   (3) Heat to 700° C. at a rate of 2° C./minute in an air atmosphere    in a nickel crucible. Dwell for 15 minutes at 700° C.-   (4) Cool to room temperature at about 50° C./minute.-   (5) Powderize pellet.

EXAMPLE III

Reaction 3(a)—Formation of Aluminum PhosphateAl(OH)₃+NH₄H₂PO₄→AlPO₄+NH₃+3H₂O

-   (1) Premix reactants in equi-molar portions using a ball mill. Thus,    1.0 mol Al(OH)₃=78.0 g and 1.0 mol NH₄H₂PO_(4=115.03) g-   (2) Pelletize powder mixture.-   (3) Heat to 950° C. at a rate of 2° C./minute in an air atmosphere.    Dwell for 8 hours at 950° C.-   (4) Cool to room temperature at about 50° C./minute.-   (5) Powderize.-   (6)

Reaction 3(b)—Formation of Lithium Vanadium Aluminum Fluorophosphate

0.9 VPO_(4+0.1) AlPO₄+1.0 LiF→LiV_(0.9)Al_(0.1)PO₄F

-   (1) Pre-mix reactants in the following proportions using ball mill.    Thus, 0.9 mol VPO₄=131.3 g, 0.1 mol AlPO₄=12.2 g, and 1.0 mol    LiF=25.9 g.-   (2) Pelletize powder mixture.-   (3) Heat to 700° C. at a rate of 2° C./minute in a nickel crucible    in either an air or inert atmosphere. Dwell for 15 minutes at 700°    C.-   (4) Cool to room temperature at about 50° C./minute.-   (5) Powderize.

EXAMPLE IV

Reaction 4—Production of Lithium Vanadium Fluorophosphate in anAlternate Formulation0.5Li₂CO₃+NH₄F+VPO₄→LiVPO₄F+0.5H₂O+NH₃+0.5 CO₂

-   (1) Pre-mix reactants in the following proportions using a ball    mill. Thus, 0.5 mol Li₂CO₃=37.0 g, 1.0 mol NH₄F=37.0 g, 1.0 mol    VPO_(4=145.9) g.-   (2) Pelletize powder mixture.-   (3) Heat to 700° C. at a rate of 2° C./minutes in an air atmosphere.    Dwell for 15 minutes at 700° C.-   (4) Cool to room temperature.-   (5) Powderize pellet.

EXAMPLE V

Reaction 5—Single Step Preparation of Lithium Vanadium FluorophosphateUsing Lithium Fluoride in a Carbothermal Method0.5V₂O₅+NH₄H₂PO₄+LiF→LiVPO₄F+NH₃+CO+1.5H₂O

-   (1) Pre-mix reactants in the following proportions using a ball    mill. Thus, 0.5 mol V₂O₅=90.94 g, 1.0 mol NH₄H₂PO_(4=115.03) g, 1.0    mol LiF=25.94 g, 1.0 mol carbon=12.0 g (Use 10% excess carbon ˜13.2    g).-   (2) Pelletize powder mixture.-   (3) Heat pellet to 300° C. at a rate of 2° C./minute in an inert    atmosphere. Dwell for 3 hours at 300° C.

(4) Cool to room temperature at 2° C./minute.

-   (5) Powderize and repelletize.-   (6) Heat pellet to 750° C. at a rate of 2° C./minute in an inert    atmosphere (e.g. argon). Dwell for 1 hour at 750° C. under an argon    atmosphere.-   (7) Cool to room temperature at 2° C./minute.-   (8) Powderize pellet.

EXAMPLE VI

Reaction 6a—Formation of Iron Phosphate0.5Fe₂O₃+(NH₄)₂HPO₄→FePO₄+2NH₃+{fraction (3/2)}H₂O

-   (1) Pre-mix reactants in the following proportions using a ball    mill. Thus, 0.5 mol Fe₂O₃=79.8 g, 1.0 mol (NH₄)₂HPO₄=132.1 g.-   (2) Pelletize powder mixture.-   (3) Heat to 300° C. at 2° C./minute in air atmosphere. Dwell 8 hours    and cool to room temperature.-   (4) Re-pelletize.-   (5) Heat to 900° C. at 2° C./minute in air atmosphere. Dwell 8 hours    and cool to room temperature.-   (6) Powderize.

Reaction 6b—Formation of LiFePO₄FFePO₄+LiF→LiFePO₄F

-   (1) Pre-mix reactants in the following proportions using a ball    mill. Thus, 1 mol FePO₄=150.8 g, 1 mol LiF=25.9 g.-   (2) Pelletize.-   (3) Heat to 700° C. at 2° C./minute in air atmosphere.-   (4) 15 minute dwell.-   (5) Cool to room temperature.-   (6) Powderize.

EXAMPLE VII

Reaction 7a—Formation of Titanium PhosphateTiO₂+NH₄H₂PO₄+0.5H₂→TiPO₄+NH₃+2H₂O

-   (1) Pre-mix reactants in the following proportions using a ball    mill. Thus, 1.0 mol TiO₂=79.9 g, 1.0 mol NH₄H₂PO_(4=115.0) g.-   (2) Pelletize powder mixture.-   (3) Heat to 300° C. at 2° C./minute in air atmosphere. Dwell for 3    hours.-   (4) Cool to room temperature.-   (5) Re-pelletize.-   (6) Heat to 850° C. at 2° C./minute in H2 atmosphere. Dwell for 8    hours.-   (7) Cool to room temperature.-   (8) Powderize.

Reaction 7b—Formation of LiTiPO₄FTiPO₄+LiF→LiTiPO₄F

-   (1) Pre-mix reactants in the following proportions using a ball    mill. Thus, 1 mol TlPO₄=142.9 g, 1 mol LiF=25.9 g.-   (2) Pelletize powder mixture.-   (3) Heat to 700° C. at 2° C./minute in inert atmosphere.-   (4) No dwell.-   (5) Cool to room temperature.-   (6) Powderize.

EXAMPLE VIII

Reaction 8a—Formation of Chromium Phosphate0.5Cr₂O₃+1.0 (NH₄)₂HPO₄→CrPO₄+2NH₃+{fraction (3/2)}H₂O

-   (1) Pre-mix reactants in the following proportions using a ball    mill. Thus, 0.5 mol Cr₂O₃=76.0 g, 1.0 mol (NH₄)₂HPO₄=132.1 g.-   (2) Pelletize powder mixture.-   (3) Heat to 500° C. at 2° C./minute in air atmosphere. Dwell 6 hours    and cool to room temperature.-   (4) Re-pelletize.-   (5) Heat to 1050° C. at 2° C./minute in air atmosphere. Dwell 6    hours and cool to room temperature.-   (6) Powderize.

Reaction 8b—Formation of LiCrPO₄FCrPO₄+LiF→LiCrPO₄F

-   (1) Pre-mix reactants in the following proportions using a ball    mill. Thus, 1 mol CrPO₄=147.0 g, 1 mol LiF=25.9 g.-   (2) Pelletize powder mixture.-   (3) Heat to 700° C. at 2° C./minute in air atmosphere.-   (4) 15 minute dwell.-   (5) Cool to room temperature.-   (6) Powderize.

Characterization of Active Materials and Formation and Testing of Cells.

Referring to FIG. 1, the final product LiVPO₄F, prepared from VPO₄ metalcompound per Reaction 1(b), appeared black in color. The product is amaterial with a triclinic crystal structure. The triclinic unit cellcrystal structure is characterized by a lack of symmetry. In a tricliniccrystal structure, a≠b≠c, and α≠βγ≠90°. This product's CuKα x-raydiffraction (XRD) pattern contained all of the peaks expected for thismaterial as shown in FIG. 1. The pattern evident in FIG. 1 is consistentwith the single phase triclinic phosphate LiVPO₄F. This is evidenced bythe position of the peaks in terms of the scattering angle 2θ (theta), xaxis. Here the space group and the lattice parameters from XRDrefinement are consistent with the triclinic structure. The values area=5.1738 Å (0.002), b=5.3096 Å (0.002), c=7.2503 Å (0.001); the angleα=72.4794 (0.06), β=107.7677 (0.04), γ=81.3757 (0.04), cellvolume=174.35 Å3.

The x-ray pattern demonstrates that the product of the invention wasindeed the nominal formula LiVPO₄F. The term “nominal formula” refers tothe fact that the relative proportion of atomic species may varyslightly on the order of up to 5 percent, or more typically, 1 percentto 3 percent. In another aspect, any portion of P (phosphorous) may besubstituted by Si (silicon), S (sulfur) and/or As (arsenic).

The LiVPO₄F, prepared as described immediately above, was tested in anelectrochemical cell. The positive electrode was prepared as describedabove, using 22.5 mg of active material. The positive electrodecontained, on a weight % basis, 80% active material, 8% carbon black,and 12% Kynar. Kynar is commercially available PVdF:HFP copolymers usedas binder material. The negative electrode was metallic lithium. Theelectrolyte was 2:1 weight ratio mixture of EC and DMC within which wasdissolved 1 molar LiPF₆. The cells were cycled between 3.5 and 4.4 withperformance as shown in FIG. 2. FIG. 2 is an Electrochemical VoltageSpectroscopy (EVS) voltage/capacity profile for a cell with cathodematerial formed with LiVPO₄F. FIG. 2 shows the results of the firstcycle with the critical limiting current density less than 0.1 milliampsper square centimeter with +10 mV steps between about 3.0 and 4.4 voltsbased upon 29.4 milligrams of the LiVPO₄F active material in the cathode(positive electrode). In an as prepared, as assembled, initialcondition, the positive electrode active material is LiVPO₄F. Thelithium is extracted from the LiVPO₄F during charging of the cell. Whenfully charged, about 0.75 unit of lithium had been removed per formulaunit. Consequently, the positive electrode active material correspondsto Li_(1-x)VPO₄F where x appears to be equal to about 0.75, when thecathode material is at 4.4 volts versus Li/Li⁺. The extractionrepresents approximately 129 milliamp hours per gram corresponding toabout 3.8 milliamp hours based on 29.4 milligrams active material. Next,the cell is discharged whereupon a quantity of lithium is re-insertedinto the LiVPO₄ F. The re-insertion corresponds to approximately 109milliamp hours per gram proportional to the insertion of essentially allof the lithium. The bottom of the curve corresponds to approximately 3.0volts.

FIG. 3 is an Electrochemical Voltage Spectroscopy differential capacityplot based on FIG. 2. As can be seen from FIG. 3, the relativelysymmetrical nature of the peaks indicates good electrical reversibility.There are small peak separations (charge/discharge), and goodcorrespondence between peaks above and below the zero axis. There areessentially no peaks that can be related to irreversible reactions,since peaks above the axis (cell charge) have corresponding peaks belowthe axis (cell discharge), and there is very little separation betweenthe peaks above and below the axis. This shows that the LiVPO₄F as highquality electrode material.

Referring to FIG. 4, the final product LiFePO₄F, prepared from FePO₄metal compound per Reaction 6(b), appeared brown in color. (Reactions 6aand 6b are carried out in the same manner as reactions 1a and 1b.) Theproduct is a material with a triclinic crystal structure. This product'sCuKα x-ray diffraction pattern contained all of the peaks expected forthis material as shown in FIG. 4. The pattern evident in FIG. 4 isconsistent with the single phase triclinic phosphate LiFePO₄F. This isevidenced by the position of the peaks in terms of the scattering angle2θ (theta), x axis. Here the space group and the lattice parameters fromXRD refinement are consistent with the triclinic structure.

The values are a=5.1528 Å (0.002), b=5.3031 Å(0.002), c=7.4966 Å(0.003); the angle α=67.001° (0.02), β=67.164° (0.03), γ=81.512° (0.02),cell volume=173.79 Å3. The x-ray pattern demonstrates that the productof the invention was indeed the nominal formula LiFePO₄F.

Referring to FIG. 5, the final product LiTiPO₄F, prepared from TlPO₄metal compound per Reaction 7(b), appeared green in color. (Reactions 7aand 7b are carried out in the same manner as reactions 1a and 1 b.) Theproduct is a material with a triclinic crystal structure. This product'sCuKα x-ray diffraction (XRD) pattern contained all of the peaks expectedfor this material as shown in FIG. 5. The pattern evident in FIG. 5 isconsistent with the single phase triclinic phosphate LiTiPO₄F. This isevidenced by the position of the peaks in terms of the scattering angle2θ (theta), x axis. The x-ray diffraction pattern was triclinic.

Referring to FIG. 6, the final product LiCrPO₄F, prepared from CrPO₄metal compound per Reaction 8(b), appeared green in color. (Reactions 8aand 8b are carried out in the same manner as reactions 1a and 1 b.) Theproduct is a material with a triclinic crystal structure. This product'sCuKα x-ray diffraction pattern contained all of the peaks expected forthis material as shown in FIG. 6. The pattern evident in FIG. 6 isconsistent with the single phase triclinic phosphate LiCrPO₄F This isevidenced by the position of the peaks in terms of the scattering angle2θ (theta), x axis. Here the space group and the lattice parameters fromXRD refinement are consistent with the triclinic structure. The valuesare a=4.996 Å (0.002), b=5.307 Å (0.002), c=6.923 Å (0.004); the angleα=71.600° (0.06), β=100.71° (0.04), γ=78.546° (0.05), cell volume=164.54Å3. The x-ray pattern demonstrates that the product of the invention wasindeed the nominal formula LiCrPO₄F.

As demonstrated by the above example, the methods described herein havesuccessfully been used to make the LiM_(1-y)Ml_(y)PO₄F compounds. Thesemethods produce products which are essentially homogeneous, single phasecompounds. Although small amounts of other materials or phases may bepresent, such does not alter the essential character of the products soproduced.

In summary, the invention provides new compounds LiM_(a)Ml_(b)PO₄F, morespecifically, LiM_(1-y)Ml_(y)PO₄F, which are adaptable to commercialscale production. The new compounds are triclinic compounds asdemonstrated by XRD analysis. The new materials demonstrate relativelyhigh specific capacity coupled to a desirable voltage range andenergetic reversibility. These properties make these materials excellentcandidates as cathode active compound for lithium ion applications. Thenew materials of the invention are easily and conveniently produced fromavailable precursors with no loss of weight, or generation of wasteproducts. The precursors can be produced by methods, such ascarbothermal reduction. In other words, this invention provides newcompounds capable of being commercially and economically produced foruse in batteries. In addition, the use of lighter non-transition metalsand elements mixed with the transition metal in the lithium metalfluorophosphate provides for structural stability and better recyclingof the lithium ions.

While this invention has been described in terms of certain embodimentsthereof, it is not intended that it be limited to the above description,but rather only to the extent set forth in the following claims.

1. A lithium metal fluorophosphate compound of the formula LiMPO₄F,wherein M is a metal with more than one oxidation state above the groundstate M⁰, made by a process comprising the step of reacting a metalcompound with a phosphoric acid derivative and lithium fluoride to formthe lithium metal fluorophosphate.
 2. The compound of claim 1, whereinthe metal compound is selected from the group consisting of Fe₂O₃,Fe₃O₄, V₂O₅, VO₂, MnO₂, TiO₂, Ti₂O₃, Cr₂O₃, CoO, Ni₃(PO₄)₂, Nb₂O₅,Mo₂O₃, V₂O₃, FeO, CO₃O₄, CrO₃, Nb₂O₃, MoO₃.
 3. The compound of claim 1,wherein the phosphoric acid derivative is selected from the groupconsisting of diammonium hydrogen phosphate and ammonium dihydrogenphosphate.
 4. The compound of claim 1, wherein the step of reacting ametal compound with a phosphoric acid derivative and lithium fluoride toform the lithium metal fluorophosphate comprises the steps of: forming amixture comprising the phosphoric acid derivative, lithium fluoride andthe metal compound; and heating the mixture at a temperature and for atime sufficient to form the lithium metal fluorophosphate.
 5. Thecompound of claim 4, wherein the heating step is carried out under areducing atmosphere.
 6. The compound of claim 5, wherein the reducingatmosphere is hydrogen gas.
 7. The compound of claim 4, wherein themixture further comprises carbon, and the heating step is carried outunder an inert atmosphere.
 8. A lithium metal fluorophosphate compoundof the formula LiMPO₄F, wherein M is a metal, made by a processcomprising the steps of: reacting a metal compound with a phosphoricacid derivative to form a metal phosphate precursor; and reacting themetal phosphate precursor with lithium fluoride to form the lithiummetal fluorophosphate.
 9. The compound of claim 8, wherein the metalcompound is selected from the group consisting of Fe₂O₃, Fe₃O₄, V₂O₅,VO₂, MnO₂, TiO₂, Ti₂O₃, Cr₂O₃, CoO, Ni₃(PO₄)₂, Nb₂O₅, Mo₂O₃, V₂O₃, FeO,Co₃O₄, CrO₃, Nb₂O₃, MoO₃.
 10. The compound of claim 8, wherein thephosphoric acid derivative is selected from the group consisting ofdiammonium hydrogen phosphate and ammonium dihydrogen phosphate.
 11. Thecompound of claim 8, wherein the step of reacting a metal compound witha phosphoric acid derivative to form a metal phosphate precursorcomprises the steps of: forming a mixture comprising the phosphoric acidderivative and the metal compound; and heating the mixture at atemperature and for a time sufficient to form the metal phosphateprecursor.
 12. The compound of claim 11, wherein the heating step iscarried out under a reducing atmosphere.
 13. The compound of claim 12,wherein the reducing atmosphere is hydrogen gas.
 14. The compound ofclaim 11, wherein the mixture further comprises carbon, and the heatingstep is carried out under an inert atmosphere.
 15. A lithium metalfluorophosphate compound of the formula LiMPO₄F, wherein M is a metal,made by a process comprising the steps of: reacting a metal compoundwith a phosphoric acid derivative to form a metal phosphate precursor;and reacting the metal phosphate precursor with lithium carbonate andammonium fluoride to form the lithium metal fluorophosphate.
 16. Thecompound of claim 15, wherein the metal compound is selected from thegroup consisting of Fe₂O₃, Fe₃O₄, V₂O₅, VO₂, MnO₂, TiO₂, Ti₂O₃, Cr₂O₃,CoO, Ni₃(PO₄)₂, Nb₂O₅, Mo₂O₃, V₂O₃, FeO, CO₃O₄, CrO₃, Nb₂O₃, MoO₃. 17.The compound of claim 15, wherein the phosphoric acid derivative isselected from the group consisting of diammonium hydrogen phosphate andammonium dihydrogen phosphate.
 18. The compound of claim 15, wherein thestep of reacting a metal compound with a phosphoric acid derivative toform a metal phosphate precursor comprises the steps of: forming amixture comprising the phosphoric acid derivative and the metalcompound; and heating the mixture at a temperature and for a timesufficient to form the metal phosphate precursor.
 19. The compound ofclaim 18, wherein the heating step is carried out under a reducingatmosphere.
 20. The compound of claim 19, wherein the reducingatmosphere is hydrogen gas.
 21. The compound of claim 18, wherein themixture further comprises carbon, and the heating step is carried outunder an inert atmosphere.
 22. A lithium mixed-metal fluorophosphatecompound of the formula LiM_(1-y)Ml_(y)PO₄F, wherein M and Ml are eachmetals and 0≦y≦1, made by a process comprising the steps of: reacting afirst metal compound with a phosphoric acid derivative to form a firstmetal phosphate precursor; reacting a second metal compound with aphosphoric acid derivative to form a second metal phosphate precursor;and reacting the first metal phosphate precursor and the second metalprecursor with lithium fluoride to form the lithium mixed-metalfluorophosphate.
 23. The compound of claim 22, wherein the first metalcompound is selected from the group consisting of Fe₂O₃, Fe₃O₄, V₂O₅,VO₂, MnO₂, TiO₂, Ti₂O₃, Cr₂O₃, CoO, Ni₃(PO₄)₂, Nb₂O₅, Mo₂O₃, V₂O₃, FeO,CO₃O₄, CrO₃, Nb₂O₃, MoO₃.
 24. The compound of claim 22, wherein thephosphoric acid derivative is selected from the group consisting ofdiammonium hydrogen phosphate and ammonium dihydrogen phosphate.
 25. Thecompound of claim 22, wherein the step of reacting a first metalcompound with a phosphoric acid derivative to form a first metalphosphate precursor comprises the steps of: forming a mixture comprisingthe phosphoric acid derivative and the first metal compound; and heatingthe mixture at a temperature and for a time sufficient to form the firstmetal phosphate precursor.
 26. The compound of claim 25, wherein theheating step is carried out under a reducing atmosphere.
 27. Thecompound of claim 26, wherein the reducing atmosphere is hydrogen gas.28. The compound of claim 25, wherein the mixture further comprisescarbon, and the heating step is carried out under an inert atmosphere.